The past two decades have seen advancements in laser technologies wherein laser pulses are routinely generated with durations on the femtosecond [...] timescale. Such pulses allow only a few cycles (oscillations) of the laser electric field for lasers with wavelengths centered in the visible to near-infrared (IR). Not only can there be marked variations in the peak electric field value, caused by varying the pulse's carrier-envelope phase (CEP), but the compression of the pulse energy to within such short durations readily allows the production of strong laser fields with peak intensities that are well into the petawatt ( 1015 W/cm2) regime.

The strong-field ionisation of atoms and molecules via light{matter interactions is a fundamental process across many research fields. Such interactions have previously been used to reveal the structure and control the dynamics of atoms, molecules and solids, and to drive processes such as lamentation and to generate attosecond [...] pulses. These interactions are highly non-linear and are difficult to model theoretically, bringing into question the ability of current theoretical models to capture all of the significant physical processes occurring during said light{matter interactions. Not surprisingly, there is often a discord between theoretical predictions and experimental data for strong-field processes, hampering experiment-theory comparison and, more worryingly, obscuring the correct physical interpretation of the experimental results. Therefore, an obvious need for accurate experimental data exists.

The gold standard for target species in atomic physics is atomic hydrogen (H). It is the simplest atomic system and is the only species for which highly-precise (limited by numerical accuracy) solutions to the three-dimensional time-dependent Schrodinger (3DTDSE) equation are possible. Atomic H serves as a test bed for various theoretical models of ionisation, however it is difficult to produce experimentally. The author of this thesis was in a unique position of having access to both a source of atomic H and a few-cycle laser with which to undertake investigations.

This thesis details two investigations of strong-field ionisation of atomic H using few-cycle light pulses. [...]